G'day

Got issues, big ones. Ive got an xf wagon.

The problem is that when applying the brakes the first time i get in the car and for about 10km the brakes want to grab, what causes this?
Ive had this problem before and i thought that it was the pads been well beyond replacement so i changed them. The problem went away straight away. Now its doing it again but the pads are still 3/4 there. Could it be a sticky caliper?
The other suggestion i was given 2day was that the shoes on the drum brakes are cactus. This doesn't surprise me. If this is the problem i can fix it quickly. I have a disc brake lsd nearly ready to go in. It has reco calipers and slotted rotars on it. Just need to find out about the master cylinder before i put it in, do i need to change the master cylinder when i swap the diffs over. If i can swap the diffs over without changeing the master cylinder this may solve the "suspected" problem but raise another question, is it safe/ advisable to run the lsd diff with the slotted rotars while the fronts are still smooth?

I know this may not make sense but any help would be greatly appreciated as the car is getting a bit dangerous to drive.

Cheers